Plants cannot survive long in hydroponics without nutrients added to the water. They might last a couple weeks on seed reserves but will yellow and die once those run out. Plain water gives roots nothing to build new cells with.
I ran an experiment with lettuce seedlings last winter to test this exact question. One tray got a full nutrient mix while the other got only plain RO water. The plain water tray looked fine for about 10 days before leaves turned pale yellow and growth stopped.
By day 14, the no-nutrient plants were dying while the fed plants had doubled in size. The difference was striking. I took photos each day and you could pinpoint the exact moment their seed reserves ran out completely.
Seeds store enough energy and minerals to fuel germination and early growth. This built in food supply gets the plant started but cannot last. Once those reserves deplete, plants need nutrients hydroponics systems must provide from the water.
There are 17 essential elements that plants must absorb to survive and grow. Carbon, hydrogen, and oxygen come from air and water. The other 14 must come from your nutrient solution. Without them, plants cannot make proteins, sugars, or new tissue.
NIH research shows that hydroponic nutrient necessity matters more than in soil growing. Soil holds nutrients in reserve that plants can tap when needed. Hydroponic systems have no buffer at all. What is in your water now is all your plants can access.
This lack of reserve makes soilless growing requirements more demanding for you. You must provide everything your plants need. Miss one element and deficiency symptoms show up within days instead of weeks.
Plain water does work fine during the first few days of seed starting. Seeds need moisture to sprout but not nutrients yet. I start all my seeds in plain water and only add nutrients once the first true leaves appear on the plants.
The signs that your plants need nutrients are easy to spot once you know them. Pale or yellow leaves mean nitrogen shortage. Purple stems suggest phosphorus problems. Slow growth with no other symptoms often points to low overall nutrient levels in your tank.
When I first started growing, I tried to save money by using weak nutrient solutions. My plants survived but grew tiny and produced almost nothing. Once I bumped up to full strength, the same varieties yielded three times as much produce.
The minimum nutrients you need depend on what you grow. Leafy greens can get by with weaker solutions around 1.0 EC. Fruiting plants like tomatoes and peppers need stronger mixes up to 2.0 EC or higher during their peak production phase.
Never try to grow a full crop on plain water thinking you can add nutrients later. By the time you see deficiency symptoms, damage has already happened. Start with proper nutrition from day one and your plants will reward you with fast healthy growth.
A friend of mine tried growing basil in just tap water to see what would happen. The plants sprouted fine but never grew past two inches tall. They sat there looking sickly for weeks before he gave up and started over with real nutrients.
Read the full article: Hydroponic Nutrient Solutions: The Complete Guide
